1. Field of the Invention
This invention relates to machine dishwashing detergent compositions and related processes.
2. Description of the Prior Art
In the art of cleaning compositions for use in cleaning hard surfaces, particularly the art of cleaning tableware and other food-soiled utensils in machine dishwashers, the problem of excessive foam buildup in the machine during operation as the result of high food soil concentrations has been largely solved by the use of alkyl phosphate ester defoamers such as monostearyl acid phosphate as disclosed in U.S. Pat. No. 3,314,891. Prior to such disclosure, machine dishwashing compositions had the tendency to foam excessively and/or leave undesirable spots and streaks on dishes and glassware. The low foaming nonionic surfactants contained in such detergent compositions were ineffective in both removing food soil and providing suitable foam control where the aqueous cleaning solution became contaminated with foam generating protein soils such as egg soil and soil from various milk products.
The generation of such foams is particularly insidious in that the cleaning action of the machine dishwasher depends to a large extent upon the effective suppression of foam generation during operation. Without effective foam suppression, the mechanical cleaning action of the machine dishwasher is reduced as the result of foam buildup in the aqueous cleaning solution so that the aqueous washing fluid which is normally impelled against the tableware in the machine dishwasher is less effective in cleaning because it is forced against the tableware at reduced pressure.
An indication of the various kinds of nonionic surfactants utilized in such machine dishwashing compositions can be found in the above patent and in U.S. Pat. No. 3,359,207. General disclosures of nonionic surfactants can be found in U.S. Pat. Nos. 2,677,700, 2,979,528, and 3,036,118. Low foaming washing and cleaning agents for use in machine dishwashing are also disclosed in U.S. Pat. No. 3,382,176. More recently, machine dishwashing detergent compositions based upon a non-phosphate salt builder have been disclosed in British No. 1,325,645; Canadian No. 941,707; U.S. Pat. Nos. 3,899,436; 4,127,496; and 4,092,258.
Recently a new series of nonionic surfactants has been disclosed, certain members of which possess relatively low cloud points as measured in a one percent aqueous solution. Such surfactants are suggested for use in the formulation of machine dishwashing detergents and generally for use where a defoamer is necessary. These new nonionic surfactants are termed TETRONIC.RTM. R polyols and are produced by the sequential block polymerization of ethylene oxide and propylene oxide utilizing, as polymerization initiator, a propoxylated ethylenediamine sold under the trademark QUADROL.RTM.. The TETRONIC.RTM. R polyols were introduced to the trade in September, 1978.
In no one of the above prior art references is there disclosed the use of a novel homogeneous blend of a conventional low foaming nonionic surfactant and a second nonionic surfactant wherein said second surfactant is characterized by a relatively low cloud point, i.e., about 10.degree. C. to about 20.degree. C. in a 1 percent aqueous solution. Said blend is useful in formulating machine dishwashing detergents which are capable of effectively controlling foaming during dishwasher operation caused by protein soil contamination.